Capital: A Critique of Political Economy (Das Kapital series Book 1)

In the same way, Marx’s theory of historical materialism does indeed include comparative economic analysis – for example an examination of the evolution of human labour, human labour productivity, social surplus product and economic growth, from slave society through feudalism to capitalism. But such comparison can result only from the analysis of specific modes of production, each with its own economic logic and its own laws of motion. These cannot be superseded by or subsumed under ‘eternal’ economic laws. We can even push the analogy to its final conclusion. If one tries to find some basic common kernel in ‘all’ anatomy, one leaves the realm of that specific science and enters another: biology or biochemistry. In the same way, if one tries to discover basic working hypotheses valid for ‘all’ economic systems, one passes from the realm of economic theory to that of the science of social structures: historical materialism.

Exchange-value appears first of all as the quantitative relation, the proportion, in which use-value of one kind exchange for use-values of another kind.6

The usefulness of a thing makes it a use-value.